[FieldTrip] Edge effect/artifact in time-frequency representation

[PAGES PORTABELLA, CARLOTA MARIA]

Dear Fieldtrip community,
I am Carlota Pagès, a Ph.D. candidate in the CBC of UPF (Barcelona).
Currently, I'm exploring the neural oscillations of music unexpectedness.

I have run time-frequency analysis on my EEG data via wavelet convolution
and applied a dB baseline correction for my different conditions. However,
when I plot the output, it appears some activity that (in my opinion) does
not look as brain-related because of its high power values and might be
masking the effects of interest (best seen in electrode Fz). When I
calculate the difference between conditions, it disappears. Therefore, it
is equally present in all conditions.
I wondered whether it might be an artifact due to a preparation of blink
(which happens right after the end of the trial) or an effect of the
baseline correction (baselines are statistically equal across
conditions). Please find the image and my script (for a single subject)
below.
Have any of you observed something similar and have a clue on what could be
causing it? And if so, what would be a good way to correct it?
Any help would be appreciated.

cfg = [];

cfg.demean = 'yes';

data_demean = ft_preprocessing(cfg, data);

% wavelet convolution

cfg = [];

cfg.method     = 'wavelet';

cfg.output     = 'pow';

cfg.foi        = 30:1:60;

cfg.width      = 10;

cfg.toi        = -0.7:0.03:1.2;

cfg.pad =  2;

cfg.trials     = data.trialinfo == 1;

wavelet_cond1 = ft_freqanalysis(cfg, data_demean);

% db normalization

cfg = [];

cfg.baseline = [-0.2 -0.05];

cfg.baselinetype = 'db';

wavelet_cond1_db = ft_freqbaseline(cfg, wavelet_cond1);

% multiplot

cfg = [];

cfg.colorbar     = 'yes';

cfg.channel = {'all', '-Fp1', '-Fp2'};

cfg.showlabels = 'yes';

cfg.layout = acticap32;

figure; ft_multiplotTFR(cfg, wavelet_cond1_db);


[image: multiplot.png]





-- 
Carlota Pagès

PhD Student
<https://www.upf.edu/web/lcc/entry/-/-/139611/adscripcion/carlota-pag%C3%A8s>
Language & Comparative Cognition Group <https://www.upf.edu/web/lcc> l Center
for Brain and Cognition <http://cbc.upf.edu/> l UPF

*Office 24.326*
*Mercè Rodoreda Building*

*c\ Ramon Trias Fargas, 25-27
<https://maps.google.com/?q=c%5C+Ramon+Trias+Fargas,+25-27+08005+Barcelona&entry=gmail&source=g>08005
Barcelona
<https://maps.google.com/?q=c%5C+Ramon+Trias+Fargas,+25-27+08005+Barcelona&entry=gmail&source=g>*
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20201214/69267b7b/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: multiplot.png
Type: image/png
Size: 97725 bytes
Desc: not available
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20201214/69267b7b/attachment.png>